bug 9458, fix Import Vcard can create multiple surnames with all selected as 'Primary'

data/tests/imp_vcard.difs

@@ -1,5 +0,0 @@
-Mismatch on file: imp_vcard.vcf
-Person: I0019  handle=0000001800000018
-  Diff on: Person, primary_name, surname list #2, primary
-    <class 'bool'>: True
-    <class 'bool'>: False

gramps/plugins/importer/importvcard.py

@@ -384,6 +384,7 @@ class VCardParser:
                 surname.set_surname(sname.strip())
                 surname.set_prefix(prefix.strip())
                 name.add_surname(surname)
+            name.set_primary_surname()
 
         if len(data_fields) > 1 and data_fields[1].strip():
             given_name = ' '.join(self.unesc(